Systems for administering liquids to a patient are widely used in clinical settings. All of these systems comprise a container for the liquid and a flow set for delivering the liquid to the patient. In general, the liquid is either allowed to drain through the flow set to the patient under the action of gravity or is pumped through the flow set. Systems Using pressure sleeves on the container are also used. Systems using a pump are referred to in this specification as "pump systems".
The rate of flow of the liquid through the system is usually set to a desired rate depending on the needs of the patient. In pump systems this may be achieved by controlling the pump rate. However, particularly when intended for intravenous administration of liquids, it is important to ensure that there will be no back flow of liquid in the tubing, that is away from the patient. To prevent this, a one-way valve is typically installed in the flow set. Further, because the container is typically mounted on a stand it is necessary to ensure that free-flow of liquid due to the liquid head will not occur when the pump is at rest. For this purpose, the valve, in addition to being a one-way valve, also needs to prevent free flow. Therefore the valve has a certain threshold pressure which is required to open it to allow flow of liquid. The threshold pressure is also known as the "cracking point". Pump systems containing such a valve are described in PCT Application WO 95/16480 and U.S. Pat. No. 5,472,420. However, incorrect valves are occasionally connected in the flow sets with serious consequences.
It is also important to ensure that the flow set, which is typically provided as an integral disposable set, is correctly connected to the pump to avoid pumping of liquid in a reverse direction, away from the patient. This is often left to the supervising staff and errors do occur. Also, flow sets occasionally fail and this is often not noticed until too late.
It is therefore an object of the invention to provide a pump system which automatically detects errors which may impair the proper functioning of the system.